Delta-sigma modulator topologies with high immunity to pattern noise

This paper addresses the problem of pattern noise encountered in single-stage delta-sigma modulators in the presence of a DC input signal. By utilizing state-space matrices, we explain the cause of these undesired cyclic patterns and show how a modulator's susceptibility to tonal behavior can be determined by inspection of the system matrix A. By example of two frequently used single-stage architectures, a 2nd and a 3rd order system, we demonstrate that simple topological modifications can render a given system immune to cyclic sequences. The two examples prove that this immunity can be achieved without visibly degrading the modulator's noise shaping capability. In fact, the modification applied to the 2nd order system even improves the quantization noise suppression.